1. Field of the Invention
The invention relates to a steering control apparatus for assisting steering of a steering wheel by driving a three-phase alternating current motor, that is referred to hereafter as a “steering assist motor”, serving as a driving source of an electric power steering apparatus.
2. Description of the Related Art
In this type of steering control apparatus, when the steering assist motor cannot be driven due to an abnormality, the steering assist motor is rotated by the steering of the steering wheel so as to function as a power generator, and as a result, a battery as direct current power source of a vehicle, for example, is charged. Steering resistance generated at this time includes both frictional resistance from a movable portion and resistance required to generate power by converting kinetic energy into electric energy. The resistance required to generate power is referred to hereafter as “power generation resistance”. Meanwhile, in a conventional steering control apparatus, a mechanical switch is provided on a power supply line connected to the steering assist motor. In this steering control apparatus, the mechanical switch is turned off when an abnormality occurs such that a motor driving circuit provided in the steering control apparatus is disconnected from the steering assist motor. As a result, the power generation resistance is removed from the steering resistance, and thus a reduction in steering resistance when an abnormality occurs can be achieved such as Japanese Patent Application Publication No. 2005-199746 “JP-A-2005-199746”.
However, a malfunction may occur in the mechanical switch due to the infiltration of foreign matter.